Radio frequency (RF) spectrum is the foundation for many wireless communications systems in use today, including radar and cellular communications systems. Specified frequency ranges in the RF spectrum, sometimes identified as bands or channels, may be allocated for use by different entities, for different purposes, or in different geographic locations. As used in this disclosure, “spectrum” refers to any frequencies, frequency bands, and frequency channels in the RF spectrum that may be used or allocated for wireless communications.
Because the available RF spectrum is finite, frequency allocations in the spectrum are highly valued and often highly regulated. In the United States, for example, the Federal Communications Commission (FCC) and the National Telecommunication and Information Administration (NTIA) regulate and manage spectrum allocations, allotments, and assignments. Frequency allocation is the process by which the entire RF spectrum is divided into frequency bands established for particular types of service. These frequency allocations are then further subdivided into channels designated for a particular service or “allotment.” Assignment refers to the final subdivision of the spectrum in which a party gets one or more frequency assignments, in the form of a license, to operate a radio transmitter on specific frequencies within a particular geographic location.
The system of spectrum allocation, allotment, and assignment is failing to keep pace with the increasing demand for spectrum. Therefore there is a need to improve how available spectrum can be efficiently allocated, allotted, and assigned in the face of growing demand. Unless otherwise noted, “allocation” is used in the present disclosure to generally refer to the process by which spectrum is allocated, allotted, and assigned to licensed users.
In view of this increasing demand for spectrum, a dynamic spectrum access (DSA) system may be used to share available spectrum among multiple users. A DSA system, for example, may include a Spectrum Access System (SAS) that manages access to a shared spectrum, such as the 3.5 GHz Federal band recently made available for shared commercial use in the United States. In another example, a DSA system may be used to share access to unlicensed spectrum, such as TV Whitespace. Coordinating and managing multi-user access to a shared spectrum present challenges in a DSA system.
As demand for spectrum grows, shared spectrum usage is becoming more common. In these environments, an SAS may control spectrum access among users assigned to different priority levels (or “tiers”) of spectrum access privileges. The SAS may implement spectrum management policies for users in each tier. For example, the SAS may be configured to protect spectrum usage by higher-priority users (e.g., “primary users”) in shared bands from interference that would result from communications by lower-priority users (e.g., “secondary users”). As used herein, a “user” may refer to user equipment (e.g., a mobile phone, etc.), or an entity or person using user equipment. In many cases where there are relatively few primary users, spectrum usage by primary users may be low. Therefore, secondary users may dominate overall usage in the spectrum. However, whether in regions with high or low primary user spectrum usage, an SAS ensures that any spectrum allocations to secondary users does not create unacceptable levels of interference with the primary users transmitting in the shared spectrum.
A key feature of many DSA systems is the ability to identify primary users so they can be protected from harmful interference from secondary users. In some circumstances, primary users remain at fixed locations and can therefore be registered in a database accessed by the SAS. In these cases, the SAS can use information from the database associated with the primary user, including location, system parameters, receiver sensitivity, filtering, antenna height, pattern, azimuth, and elevation, to ensure that any secondary user assignment does not cause harmful interference to the primary user.
In other circumstances, primary users may not be static and may be mobile. Further still, primary users may be unable to share their location and/or system parameters with an SAS for security or confidentiality reasons. An example of one such primary user of this type includes primary users operating federal radar systems on sea-going military vessels (e.g., military ships and submarines). To protect these primary users from secondary user interference, an SAS requires a spectrum sensing capability, for example, using an Environmental Sensing Capability (ESC) system, to determine when and where the primary user is operating and, optionally, determine system parameters associated with the primary user. The SAS would leverage ESC system reports to ensure an acceptable quality of service for primary users transmitting in the shared spectrum, while also maximizing throughput and capacity for the secondary users using the same spectrum. Moreover, the ESC system may provide operational security (OPSEC) and communications security (COMSEC), for example, to avoid compromising the locations and/or system parameters of the primary users while also protecting them from secondary-user interference in the shared spectrum.